Southern resident killer whales

The research vessel Noctiluca of the Northwest Fisheries Science Center in close proximity to a killer whale

The southern resident killer whales (SRKW) represent the smallest of four resident communities within the Northeastern portion of North America Pacific Ocean. It is the only killer whale population listed as endangered by the U.S. Fish & Wildlife Service. It is currently protected under the Endangered Species Act as of 2005.[1] In Canada the SRKW are listed as endangered on Species at Risk Act Schedule 1.[2] They are commonly referred to as the "orcas of the Salish Sea",[3] "fish-eating orcas", or the "SRKW" population. Unlike other resident communities, the SRKW is only one clan (J) that consists of 3 pods (J, K, L) with several matrilines within each pod.[4] As of September 2017 there are only 76 individuals that make up this small population.[5] The world's oldest known killer whale, Granny or J2, had belonged to and led the J pod of the SRKW population. As of October 2016, she is missing and presumed deceased. [6] J2 was estimated to have been born around 1911, which means she would have been 105 years old at the time of her death, and the oldest known Orca to date.[7]

Photo identification over the last 38 years has allowed researchers to track the southern resident population quite accurately, such as the Orca ID site[8] offered through the Center for Whale Research. Their population is built upon a matrilineal system where these strong hierarchical groups of individuals are connected by maternal descent. Each matriline consists of a female, her sons and daughters and the offspring of her daughters; averaging anywhere from one to seventeen individuals and one to five generations within each of these matrilines.[4] Pods are groups of matrilines that share a maternal ancestor, in which the southern residents consist of three pods. The number of individuals changes due to birth and deaths.

The Orca Network provides a list (last updated September 2017). The following is the basic social structure:[9]

Community

Southern Resident

Clan

J

Pods

J Pod (23 members)

K Pod (18 members)

L Pod (35 members)

Matrilines

J2(believed deceased as of October 2016), J4, J5, J7, J10, J11, J32 (found dead on a beach on Vancouver Island on December 4, 2014.)

K4, K7, K8, K11, K18

L2, L4, L9, L12, L21, L25, L26, L28, L35, L37

In 2014, L120 was born into L pod but didn't survive more than a month. In late 2014, J50 Scarlet was born into the J pod. After a lot of speculation, J16 Slick was confirmed to be J50's mother, making the 42-year-old the oldest ever recorded orca mother. The gender of the calf is confirmed to be female.[10]

In February 2015, two new calves were spotted, a male calf in J pod, designated J51 Nova, and another male in L pod, designated L121 Windsong. J51's mother is ten-year-old J41 Eclipse and L121's mother is twenty-year-old L94 Calypso. A fourth calf, designated J52 was born in March 2015 to J36 Alki, who is J16's daughter. In early 2016, J52 Sonic was confirmed to be male, however he died in September 2017, presumably from starvation.[11] . Since 1998, 40 orca calves have been born to J, K & L pods and survived, while 72 orcas have gone missing (presumed dead) or have been confirmed dead.[12]

Similar dialects amongst pods create the social grouping called "clans". It is believed that the more similar their dialect is within the pods, the more closely related they are. The southern dialect is very different from that of other communities. For instance, northern residents use whistles as their main type of close-range communication and the southern residents use whistles for regular social interactions and long-range communications. Southern residents appear to be much more vocal but it could be due to their vocal usage during travel and the fact that they seem to travel more than the northern residents.[4]

Southern residents are fish-eating orcas that appear to prefer the Chinook salmon to other fish species. From visual sources, necropsy, and feces collection, the following food preferences have been reported:[4]

The depletion of large quantities of fish in the marine environments, while personal fishing in the salmon’s upstream spawning grounds have further depleted stock replenishment.[15] Aquaculture has had a negative effect on world fish supplies,[16] including through the spread of pathogens to the wild fish stock. A study also found that Chinook salmon found in South Puget Sound have less fat than those farther north, causing an increased need for consumption.[17]

Northwest killer whales are among the most contaminated marine mammals in the world, due to the high levels of toxic anthropogenic chemicals that accumulate in their tissues.[18] Implicated in the decline of Orca populations in the Pacific Northwest, these widespread contaminants pose a large problem for conservation efforts. While many chemicals can be found in the tissues of Orca, the most common are DDT, an insecticide, polybrominated diphenyl ethers, or PBDEs and polychlorinated biphenyls, or PCBs.[19] Each of these have detrimental physiological effects on orca,[20] and can be found in such high concentrations in dead individuals that those individuals must be disposed of in hazardous waste site.[21]

Correlative evidence shows orca may be vulnerable to effects of PCBs on many levels. Research has identified PCBs as being linked to restricting development of the reproductive system in orcas and dolphins.[22] High contamination levels leads to low pregnancy rates and high mortality in dolphins. Further effects include endocrine and immune system disruption, both systems being critical to mammalian health and survival.[20] A study examining 35 Northwest orcas found key genetic alterations that caused changes to normal physiological functions.[23] These genetic level interferences, combined with the varied effects of PCBs at other physiological levels, suggest these contaminants may be partially responsible for declines in Orca populations.

Noise and crowding from tour boats and larger vessels interrupt foraging behavior, or scare away prey. The noise can mask echolocation causing difficulty with catching prey.[24] Also, the sonar used by some ships and submarines is enough to cause hemorrhaging, and subsequently, death in some individuals[25]

^O'Neill, S, and J West. "Marine Distribution, Life History Traits, and the Accumulation of Polychlorinated Biphenyls in Chinook Salmon from Puget Sound,Washington." Transactions of the American Fisheries Societies. 138.3 (2009): 616-32.